Such a microscope is known, for example, from German Patent DE 38 26 069 C2. In carrying out diagnostic services or surgeries using a stereoscopic microscope, for example in ophthalmology, neurosurgery, etc., microscopes with a weak enlargement are usually being used. These have separate beam paths in order to enable a stereoscopic viewing of the surgery field. Ocular systems are thereby used, each including an ocular tubus forming a telescope. Furthermore, a common lens is used for both beam paths, in which lens is provided in most cases a common convex lens.
The beams or rays enter in such a microscope through the lens. The beams are guided parallel through the lens systems and are fed to the magnification changer. The beams exit from the changer and are in turn focused in parallel and fed to the respective ocular system or tubus.
In viewing the inside of the eye, one must note that due to the lens of the eye itself a laterally transposed image of the inside of the eye is viewed by the microscope. In order to eliminate this transposition or reversal, and in order to show tne image in the correct manner, an image reversal and also a change of the beam paths, namely an exchange of the right and left beam path, must be carried out in the area of the microscope. The reversal lens system provided in the microscope is used for this purpose.
It is often necessary during an eye surgery or examination that the viewer alternately view two well defined areas of the inside of the eye. The focal point of the lens must thereby be shifted in the presently existing microscopes through new focusing. The new focusing requires in each case some seconds. In particular, in the case of longer surgeries or also eye examinations, the time needed for the refocusing at a repeated change of the viewing planes cannot be neglected.
This problem occurs in particular also when an optic system is used, as is known, for example, from DE 298 19 341.8. Such an optic system is used to view the fundus of the eye, in particular of the retina. The optic system creates a first image in a point in front of the optic system. In order for the viewer to be able to view through the microscope this first image created in front of the optic system, the lens of the microscope must be focused onto this first image.
When the viewer now wants to change between the viewings with the optic system or without the optic system, the microscope must, after the optic system has been removed from the beam path, be newly focused. Thus a new focusing is necessary with each change of viewing with or without the optic system. A microscope is known from WO 98/20378, in which above and/or below the reversal lens system together with said reversal lens system lenses are moved into the beam path, which change the focusing of the microscope so that, when an optic system is inserted into the beam path, the image created in front of the optic system can be clearly recognized. A magnification changer is interpositioned in most stereoscopic microscopes so that it is possible to pull also smaller cutouts enlarged from an image. Tf a reversal lens system with a fixedly attached lens is now swung into the parallel beam path, then the compensation of the distance between the earlier focused point and the image created before the optic system, which compensation is caused by the fixedly attached lens, can be utilized only for a very specific adjustment in the magnification changer. The reason or cause for this is that the parallel beam path is changed in the reversal lens system by inserting the lenses. Whereas if travel occurs in all possible areas through the magnification changer, then a blurred, not usable image is created in almost all areas through the decentration.